The present disclosure relates to systems and methods for characterizing fluids in subterranean formations during various treatment operations therein.
Hydraulic cement compositions are commonly utilized in subterranean operations, particularly subterranean well completion operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipe strings such as casings and liners are cemented in well bores. In performing primary cementing, hydraulic cement compositions are pumped into the annular space between the walls of a well bore and the exterior surface of the pipe string disposed therein. Often one or more other fluids (e.g., drilling muds, spacer fluids, etc.) may be present in the well bore, but the cement composition and/or other fluids or equipment used in the cementing operation may be introduced into the well bore to displace those fluids so that the cement composition may fill the annular space. Once in place, the cement composition is permitted to set in the annular space, thereby forming an annular sheath of hardened substantially impermeable cement therein that substantially supports and positions the pipe string in the well bore and seals the exterior surfaces of the pipe string and the walls of the well bore. Such pipe strings within a well bore in a subterranean formation are often used, among other purposes, to ensure that the borehole does not collapse once it is drilled and that sensitive areas of the formation are protected and isolated. Thus, cement placement and the strength of both cement bonds (i.e., with the casing and with the walls of the well bore) are important to the integrity of the well. The presence of small amounts (e.g., layers or pockets) of other fluids between the cement and the casing or well bore walls can form voids in the cement or otherwise compromise the strength of the cement bond with those surfaces.
Various techniques and tools have been used in the art to evaluate the bond between casing strings and the cement placed in the wellbore annulus. In some cases, cement evaluation logs or cement bond logs may be generated by using acoustic sonic or ultrasonic tools to apply acoustic pulses to the casing to make it resonate in its thickness mode, and measuring the energy level (attenuation) of the decaying reflected wave. Good cement bonds to casing typically produces a rapid damping (higher impedance) of the resonance, while poor cement bonds typically result in longer resonance decay (lower impedance). However, these impedance measurements are only an indirect “proxy” for the bond of the cement, and do not directly detect the presence of fluids or spaces between the cement and the casing string or well bore. The use of these acoustic tools also requires additional interventions into a well, which may be costly and/or delay further operations at the well.
While embodiments of this disclosure have been depicted, such embodiments do not imply a limitation on the disclosure, and no such limitation should be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.